The invention relates to a method for implementing switching in the time domain, and to a method for implementing switching in the space domain, for signals of several different levels of hierarchy, the signals having a common frame structure. An example of such a frame structure is the frame structure of an STM-1 signal used in the SDH system; this frame structure will be illustrated in greater detail below.
The method of the invention can thus be used in both time and space switches. In this connection, the term time switch refers to a device capable of switching the contents of any time slot in the frame structure of an incoming signal to any time slot in an outgoing frame structure (switching in time). In addition to a time switch, this device can also be called a time slot interchanger. The term space switch, in turn, refers to a switch capable of connecting any incoming line to any outgoing line (switching in space).
In known switching methods, the switching of e.g. the tributary unit groups (TU-12, TU-2, TU-3) of an STM-1 frame is implemented by giving switching instructions separately to 3, 21 or 63 columns by starting the switching from column 13 on TU-3 level and from column 19 on TU-2 and TU-12 levels. It has thus been possible to effect the switching on one level at a time. Another way has been to switch columns 19 to 270 in blocks of 63 columns, and to give switching instructions separately to columns 13 to 18 on the TU-3 level. In this way it has been possible to effect cross-connection on all three of the levels at the same time.
The drawback of the known switching methods is, however, that, in practice they entail fairly complicated equipment.